Memory (lecture 4)

Thoth Mnemosyne Minerva

God/dess of learning, memory & wisdom

Memory in oral culturesMemory was essential for passing of knowledge: person to person & generation to generation.

Memory was the fourth of the five traditional canons of rhetoric, the others being invention, arrangement, delivery, and style. Memory aided by process of architectural mnemonic known as Cicero’s technique: parts of the speech were associated with spatial details.

Memory in literate cultures

Writing: externalized the memory.Electronic media: provides fast access to both

verbal and graphical data bases (“the virtual Cicero’s technique”).

Eric Havelock: "a modern student thinks he does well if he diverts a tiny fraction of his psychic powers to memorize a single sonnet of Shakespeare. In stead, he pours his energy into search and reading….

Memory is extended to artificial fast accessible devices (soon directly connected to brain).

Memory as a process

Cognitive Ψ: Three stages of memory.Biological Ψ: Stages in same/different brain sites? Neuronal mechanisms of memory? Life time storage?

Duration of memory: cognitive Ψ

Sensory memory: Vast amount of sensory information in five modalities kept for very short time.

Working memory/short-term memory: Rather limited information kept for short time in conscious mode.

Long-term memory: Vast amount of information in subconscious mode.

Duration of memory: biological Ψ

Short Working-memory: different sites of frontal cortex, can we be aware of all?

Long-term memory: migration of information from hippocampus to cortex, amnesia in HM patient.

Technique: experiments by nature & functional imaging.

Content of memory

Cognitive Ψ: Explicit memory: conscious recollection of events tagged with time and place. Implicit memory: skills with no conscious recollection of details.

Biological Ψ: Explicit memory: evolution-wise recent brain structures, cortex & hippocampus. Implicit memory: evolution-wise old brain structures.

Conclusions so far

Memory is mediated by multiple brain sites.Each site: Is governed by the three stages of memory: parallel – distributed processing. Processes different content: memory disintegrates the environment. Storing capacity seems to be unlimited except of working-memory. Stores with different time constant.

Working memory (1)

Encoding:

Phonological buffer in L-hemisphere.Semantic buffer in L-hemisphere.Spatial buffer in R-hemisphere.

Identity of the letter

Position of the letter

Working memory (2)

Storage:Low capacity: only 7±2 bits of information.

Disappointed? Don’t despair: LTM enables chunking and capacity increases to 7±2

chunks of information.Many working-memory sites? Fast forgetting due to ‘decay’ and ‘displacement’

(high throughput).

Working memory (3)

Retrieval: Easy with minimal mistakes.Decision time increases with # of items, i.e., serial

processing.

Decision time paces the swiftness of conscious mental computations, slow thinking!!!

From working-memory to LTM (1)

Maintenance rehearsal in WM: prevents a decay in a reverberating circuitry.

From working-memory to LTM (2)

In a free recall task:elaborative rehearsal helps to encode information in LTM.

LTM (1)

Encoding:Meaning – the remembered idea.Elaborate on meaning to add connections between

items. Exact wording.Sensory impressions: phonological, visual, smells…

LTM (2)

Storage:Initial store in hippocampus and later migration to

various cortical sites.Hippocampus and the surrounding cortex: cross-

referencing between the many store sites. Hippocampus as a cognitive map includes the past

and future (prospective) events.

The many LTM cortical sites

LTM (3)

Storage:New memories are consolidated over period of months and more.

LTM (4)

Retrieval:Effortful process – on “tip-of-the-tongue”.Retrieval cues help - recognition vs. recall.Failures due to association of one cue with

several items:

* Retroactive interference.

* Proactive interference.

Retrieval cues as gateways to LTM

השראת הגברה ארוכת טווח

(LTP כמנגנון )שינוי סינפטי

בודד: פולס בדיקהפולסים: רצף למידה

Lessons from amnesia

Hippocampus removed bilaterally.Spared working-memory.Anterograde amnesia for explicit-episodic

memory. Partial retrograde amnesia for explicit-

episodic memory.Other memories spared.

A variety of memories

Priming

Memory aids

END